Sex doesn’t always sell when it comes to advertising, a marketing research study has found.

Although gorgeous models are routinely used to peddle all sorts of consumer goods, there are times when their attractiveness can hurt.

The study found that stunning models are more persuasive than less attractive people in ads promoting products like shampoo or disposable razors, but when it comes to laptops and other high-end goods, people care about the credibility of the message, not the comeliness of the messenger.

“If the customer has time to process the ad, and the attractive model doesn’t fit, it’s almost like this bias detector goes off,” researcher Paul Herr said.

His report will appear in next month’s issue of the Journal of Consumer Research.